Method of operating the power train of a vehicle

Abstract

A method of operating a drive-train of a vehicle having a drive engine, a motor vehicle transmission, at least one drive axle and a further axle that can be engaged to drive. In context of a function, a connection between the drive engine and the at least one drive axle of the vehicle is automatically interrupted, and the function is automatically activated when certain conditions exist. For the activation of the function, a service brake of the vehicle must be actuated and, as a condition, the vehicle must be stopped. To check whether operation of the vehicle in the all-wheel mode is necessary, when the function is carried out, a brake pressure is determined and, if the brake pressure exceeds a brake pressure limit value, the driving engagement of the further axle is carried out automatically as the function is deactivated for re-starting the vehicle.

1 - 12 . (canceled) 
     
     
         13 . A method for operating a drive-train ( 1 ) of a motor vehicle comprising a drive engine ( 2 ), a motor vehicle transmission ( 4 ), at least one drive axle ( 6 ), and a further axle ( 18 ) that is drivingly engagable, the method comprising:
 automatically interrupting, in a context of a function, a connection between the drive engine ( 2 ) and the at least one drive axle ( 6 ) of the motor vehicle, the function being automatically activated when certain conditions exist, and the certain conditions for activating the function comprising activation of a service brake ( 11 ) of the motor vehicle and braking the vehicle to rest,   determining a brake pressure (p Brems ) when the function is carried out, and   if the brake pressure (p Brems ) exceeds a brake pressure limit value (p Grenz ), automatically carrying out the driving engagement of the further axle ( 18 ) as the function is deactivated for re-starting the motor vehicle.   
     
     
         14 . The method according to  claim 13 , further comprising, if a speed limit (v Anfahr ) is exceeded after re-starting, automatically interrupting the driving connection of the further axle ( 18 ). 
     
     
         15 . The method according to  claim 13 , further comprising parameterizing the brake pressure limit value (p Grenz ) as a function of a mode of operation of the motor vehicle. 
     
     
         16 . The method according to  claim 15 , further comprising determining the mode of operation of the motor vehicle by recognizing components that are connectable to the motor vehicle and which increase a total weight of the motor vehicle. 
     
     
         17 . The method according to  claim 16 , further comprising control-technologically connecting the components to the motor vehicle by a bus system ( 17 ). 
     
     
         18 . The method according to  claim 13 , further comprising detecting the brake pressure (p Brems ) of at least one brake circuit of the service brake system ( 11 ). 
     
     
         19 . The method according to  claim 13 , further comprising effecting a separation and re-establishment of the connection between the drive engine ( 2 ) and the at least one drive axle ( 6 ) of the motor vehicle via a starting element ( 3 ) located between the drive engine ( 2 ) and the motor vehicle transmission ( 4 ). 
     
     
         20 . The method according to  claim 13 , further comprising using a clutch unit ( 21 ) to control engagement of the further axle ( 18 ). 
     
     
         21 . The method according to  claim 13 , further comprising using one of an agricultural or a municipal utility vehicle as the motor vehicle. 
     
     
         22 . A control unit ( 13 ) for a drive-train ( 1 ) of a motor vehicle comprising:
 a device for regulating a function for separating a connection between a drive engine ( 2 ) and at least one drive axle ( 6 ) of the vehicle,   the device being designed for automatically controlling a clutch unit ( 21 ) for drivingly connecting a further axle ( 18 ) to the drive engine ( 2 ) and a motor vehicle transmission ( 4 ),   the device activating a function in the drive-train ( 1 ) which brings about a separation of a connection between the drive engine ( 2 ) and the at least one drive axle ( 6 ) of the vehicle,   a service brake ( 11 ) of the vehicle being actuatable and the vehicle being braked to a rest to activate the function, and   when carrying out the function, a brake pressure (p Brems ) being applied to the service brake for braking the vehicle to the rest, the brake pressure being determinable, and the further axle ( 18 ) being automatically engaged when the brake pressure exceeds a brake pressure limit value (p Grenz ).   
     
     
         23 . The control unit ( 14 ) according to  claim 22 , wherein the control unit carries out a method of operating the drive-train ( 1 ) of the vehicle, the method including: automatically interrupting, in a context of the function, the connection between the drive engine ( 2 ) and the at least one drive axle ( 6 ) of the vehicle, the function being automatically activated when certain conditions exist, and the certain conditions for activating the function including activating the service brake ( 11 ) and braking the vehicle to rest; determining the brake pressure (p Brems ) when the function is carried out; and, if the brake pressure (p Brems ) exceeds the brake pressure limit value (p Grenz ), carrying out the driving engagement of the further axle ( 18 ) automatically as the function is deactivated for re-starting the motor vehicle. 
     
     
         24 . The control unit ( 14 ) according to  claim 23 , in combination with a computer program product by which the method of operating the drive-train ( 1 ) of the vehicle can be carried out, wherein a routine for activating the function by corresponding control commands stored by software means is implemented. 
     
     
         25 . The control unit ( 14 ) and the computer program product according to  claim 24 , in combination with a data carrier on which the computer program product is stored. 
     
     
         26 . A method of operating a drive-train of a motor vehicle, the vehicle having a drive engine, a transmission, at least one drive axle and a further axle that is drivingly engagable, the method comprising:
 determining, via a control unit, whether a service brake of the motor vehicle has been actuated and whether the vehicle is braked to a stop;   automatically activating a function, via the control unit, if the service brake is actuated and the vehicle is braked to a stop;   in a context of the function, automatically disengaging a starting element to interrupt a connection between the drive engine and the at least one drive axle of the vehicle;   determining, via the control unit, a brake pressure when the function is carried out;   comparing, via the control unit, the determined brake pressure to a brake pressure limit value; and   if the brake pressure exceeds the brake pressure limit value, once the function is deactivated, automatically engaging a clutch to drivingly connect the further axle for re-starting the motor vehicle.